High output spring brake actuator

ABSTRACT

Disclosed is a diaphragm-based spring brake actuator assembly which allows for the delivery of more force to the push rod without increasing the size of the actuator unit. The invention allows for the use of a stronger heavy main compression spring in the emergency brake chamber to provide greater emergency or parking brake force to the push rod. The invention also allows the service brake chamber to operate more efficiently when braking pressure is introduced. These functions are accomplished through modifications in the design of the actuators which allow for the deployment of a larger pressure plate inside either the emergency housing or the service brake housing, or both, allowing delivery of more force to the push rod of the actuator; and are made possible in actuator units having the same dimensional profile as existing weaker units.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to braking systems for heavy dutyvehicles, and in particular to an improved diaphragm-based spring brakeactuator which provides significantly increased braking force from aspring brake assembly having a size that is the same as or smaller thanexisting brake assemblies.

[0003] 2. Description of the Prior Art

[0004] Various forms of pneumatic vehicle spring brake actuators havebeen introduced over the years primarily for use in the truckingindustry. A typical double diaphragm air brake actuator includes twoportions: an operator controlled service brake portion which is used forslowing or stopping a vehicle, and an emergency or parking brake portionwhich automatically engages when air pressure is removed. A typicalservice brake portion is characterized by a closed housing whichcontains a movable diaphragm stretched across the inside. One side ofthe diaphragm is closely associated with a centrally located pressureplate attached to a slidable push rod which extends out of the housingfor attachment to the brakes of the vehicle. On the other side of thediaphragm a sealed chamber is formed within the housing.

[0005] An opening is provided in the sealed service brake chamber forconnection to a pneumatic (air) pressure source usually provided by anon-board air compressor. The brakes of the vehicle can be applied byintroducing sufficient pneumatic pressure into the sealed chamber to actagainst the service brake diaphragm which moves the plate, pushing thepush rod out. A small return spring is ordinarily provided inside theservice brake housing around the push rod and adjacent to the pressureplate to urge it to retract when the air pressure behind the diaphragmis reduced.

[0006] A typical emergency brake portion of an air brake actuator isattached in axial alignment with or made a part of the service brakeassembly. The emergency brake is a separate closed housing whichcontains a heavy main compression spring and a second movable diaphragmcreating a second sealed chamber. The emergency brake diaphragm is incontact with a second pressure plate which is also attached to ordirectly associated with the slidable central push rod of the servicebrake.

[0007] The second sealed chamber is formed inside the emergency brakehousing on one side of the diaphragm, and the heavy main compressionspring is deployed on the opposite side. As with the service brake, thesealed chamber of the emergency brake is connected to the on-boardpneumatic source of the vehicle. As long as sufficient air pressure isprovided to the sealed chamber, the diaphragm in the emergency brakewill remain fully extended thereby compressing the large spring.However, should pressure fall, or should there be a leak in the sealedchamber, the diaphragm will be unable to hold the large compressionspring in place. When this occurs, either slowly or quickly, the largecompression spring will move the second pressure plate causing the pushrod to be extended out thereby applying the brakes of the vehicle.

[0008] Under normal conditions, when the vehicle is parked, the airpressure to the emergency brake portion is cut off causing the largecompression spring to apply the brakes.

[0009] In the transportation industry, it is becoming ever moredesirable to provide more powerful spring brake actuators withoutchanging their size. Increasing load sizes, new regulations and otherfactors have created a need for additional power in a spring brake withthe same dimensional profile as existing double diaphragm spring brakes.

[0010] A stronger spring brake which takes up the same or a smallerspace can result in great savings in the transportation industry. Underpresent regulations, a loaded truck must be able to apply its brakes andhold its position on a twenty percent (20%) grade. For many heavyvehicles, in order to accomplish this requires additional brakeactuators and/or additional axles with brake actuators on them. Withstronger brake actuators, fewer of them are needed to bring or hold sucha vehicle at rest, thereby saving the cost of the additional brakeactuators and/or additional axles.

[0011] There is also a need for a more powerful spring brake which fitsinto a smaller space. This need is driven by such factors as theinstallation of vehicle air suspensions, lowered floor heights, shorterwheel bases, and the addition of new and bulky chassis equipment. All ofthese factors compete for the same space occupied by the spring brake.

[0012] A spring brake assembly of smaller size which provides the samepower as a larger assembly will also reduce weight and cost. A trucktractor and semi trailer may use 8 spring brake actuators on its axles.Replacing these with smaller units having the same strength that are twopounds lighter will reduce the weight by 16 pounds. While this may notseem significant at first blush, a liquid hauling vehicle is frequentlyloaded to the exact legal limit. Over the life of that vehicle, the 16pound reduction will convert to thousands of dollars of hauling revenue.

[0013] Stronger brake assemblies deployed in the same space can improvethe stopping characteristics of a vehicle thereby potentially increasingthe gross vehicle weight allowance for the vehicle (i.e. more payload).

[0014] Existing service brake assemblies have been designed forattachment to the brake system of a heavy duty vehicle. The end of theservice brake push rod is typically attached to a clevis which is, inturn, attached to the end of a slack adjuster arm located on a cam shaftwhich makes up part of the foundation brake of the vehicle. The push rodis moved in and out of the service brake assembly using pneumaticpressure as described above in order to operate the brakes of thevehicle. As this occurs, in some situations the push rod and clevis movethe end of the slack adjuster through a slightly arcuate path around thecam.

[0015] For decades, the pressure plates used in existing diaphragm-basedspring brake actuators have been relatively small in comparison to theoverall profiles of these units. In a typical brake actuator, thepressure plate in the service brake chamber has approximately the samediameter as the pressure plate in the emergency brake chamber. The edgesof such pressure plates have traditionally been restricted to thecentral portion of the brake chamber, presumably to allow sufficientspace around the edges of the plates for the diaphragm to fold overitself. However, these traditional wide tolerances that have developedover time are far more than is necessary for the diaphragm to functionproperly, and have unnecessarily limited the sizes of the pressureplates used, and therefore unnecessarily inhibit the potential forcethat can be delivered to the push rod by the spring brake actuator.

SUMMARY OF THE INVENTION

[0016] The present invention is a departure from traditionaldiaphragm-based spring brake actuator assemblies which allows for thedelivery of more force to the push rod without increasing the size ofthe actuator unit. One embodiment of the invention allows for the use ofa stronger heavy main compression spring in the emergency brake chamberto provide greater emergency or parking brake force to the push rod.This is accomplished through novel changes to the design of theemergency brake chamber which allow it to more efficiently hold off thespring. A stronger emergency spring gives the brake actuator a greatercapacity to hold a vehicle in place while parked on a grade. Anotherembodiment of the invention employs similar novel changes to the designof the service brake chamber which allow it to operate more efficientlywhen braking pressure is introduced.

[0017] In the present invention, the pressure plate deployed insideeither the emergency housing or the service brake housing, or both, issignificantly larger than the corresponding plate(s) found in existingunits having the same dimensional profile. The plate(s) of the presentinvention have a greater diameter and a larger circumference therebydefining a larger area.

[0018] With respect to the emergency spring brake, the size of thepressure plate is directly proportional to the amount of force needed tohold off the large compression spring in the emergency brake housing.According to the formula F=PA, the force (F) exerted against thecompression spring is equal to the amount of pressure (P) exerted by thechamber multiplied by the area (A) of the pressure plate over which itis exerted. Thus, increasing the size of the pressure plate increasesthe area (A) over which the pressure (P) is exerted, thereby increasingthe force (F) against the spring. For illustrative purposes and by wayof example only, and without limiting the scope of the appended claimsherein, a pressure (P) of 60 pounds per square inch (60 psi) exertedagainst a pressure plate in the emergency brake housing having an areaof 30 square inches results in a force of 1,800 pounds. In this example,if the area of the pressure plate is increased to 35 square inches, theresulting force of the spring that may be held off increases to 2,100pounds. Thus, by simply increasing the surface area of the pressureplate, in this example an emergency brake spring that is over 14%stronger may be used (i.e. held off). Typical increases provided by thepresent invention are in the range of about twenty percent (20%).

[0019] The availability of higher pressure (P) will also increase theamount of force (F) available to hold off the emergency brake spring.Thus, by increasing the surface area (A) of the pressure plate alone orin conjunction with increasing the available pressure (P), a muchstronger spring may be used in the emergency brake.

[0020] With respect to the service brake, the size of the pressure platetherein is directly proportional to the amount of force applied to thepush rod. Again, using the formula F=PA, the force (F) applied to thepush rod is equal to the amount of pressure (P) exerted by the chambermultiplied by the area (A) of the pressure plate over which it isexerted. Thus, increasing the size of the pressure plate increases thearea (A) over which the pressure (P) is exerted, thereby increasing theforce (F) applied to the push rod. For illustrative purposes and by wayof example only, and without limiting the scope of the appended claimsherein, a pressure (P) of 60 pounds per square inch (60 psi) exertedagainst a pressure plate in the service brake housing having an area of30 square inches results in a force of 1,800 pounds applied to the pushrod. In this example, if the area of the pressure plate is increased to35 square inches, the resulting force applied to the push rod increasesto 2,100 pounds. Thus, by simply increasing the surface area of thepressure plate, in this example the service brake becomes 14% moreefficient (i.e. stronger). Typical increases provided by the presentinvention are in the range of about twenty percent (20%).

[0021] The present invention facilitates increasing the size of theeither the emergency brake pressure plate or the service brake pressureplate, or both, by incorporating one or more of the following features.First, the cylindrical walls of the spring brake housing may be mademore vertical, more parallel to the orientation of the push rod, and/ormore nearly perpendicular to the orientation of the pressure plateinside the housing. Next, the space between the outside circumferentialedge of the pressure plate and the inside of the cylindrical wall of thebrake housing (this space sometimes hereafter referred to as the “gap”)may be reduced to a size that is as small as about two and one half (2½)times the thickness of the diaphragm material, or even smaller (e.g 2¼times said thickness), thereby providing room for a larger pressureplate. Next, the diaphragm itself may be made of very thin material inorder to further minimize the size of the above described gap in orderto maximize the size of the pressure plate. Next, axial movement of themain compression spring may be minimized by minimizing side load exertedby said spring. This is accomplished by grinding down a portion of thesurfaces of the end spring coils (the coils at the top and at the bottomof the spring) so that these coils seat more predictably against thehousing and pressure plate. Finally, configuring the shape of thepressure plate to nest with an adaptor plate located on the centralshaft of the brake actuator helps keep the pressure plate in centralalignment. A bushing/seal retainer may also be employed in the center ofthe spring housing to help align the larger pressure plate in order toprevent it from drifting sideways. Each of these features, used alone orin conjunction with each other, allows for deployment of a largerpressure plate which can then be used to hold off a stronger spring inthe emergency brake housing, or to provide more force to the push rod inthe service brake housing.

[0022] The use of more vertical cylindrical walls in the presentinvention increases the interior cross sectional area of the emergencybrake housing, thereby allowing for the surface area of the pressureplate to also be increased. This is accomplished without raising theheight or width of the cylinder; thus, the overall profile of the brakeactuator remains the same.

[0023] Through experimentation, it has been determined that the size ofthe pressure plate may be increased until the above-described gapbetween the circumferential edge of the pressure plate and the insidewall of the housing is as small as two and one half (2½) times thethickness of the diaphragm material without any significant degradationin diaphragm performance. Existing brake actuators unnecessarily providemuch larger gaps between the edges of the pressure plate and the wallsof the housing which range from four and one half (4½) up to seven (7)times the thickness of the diaphragm material. In the present invention,the surface area of the pressure plate that is gained by closing thisgap is substantial. When combined with more vertical cylindrical walls,even more space is made available for the pressure plate.

[0024] The use of thinner diaphragm material allows the edges of thepressure plate to extend even closer to the cylindrical walls of thehousing, thereby allowing for an even greater increase in the surfacearea of the pressure plate. Existing brake actuators use diaphragmmaterials having an average thickness of 0.125 inches, a tight onehaving a gap of 0.57 inches between the edge of the pressure plate andthe wall of the housing (about 4½ times the thickness of the diaphragm).This gap may be reduced, as above, in the present invention down to assmall as 2½ times the diaphragm thickness, or even smaller (e.g.2½×0.125=0.3125 inches; 2¼×0.125=0.2813 inches). For illustrativepurposes and by way of example only, and without limiting the scope ofthe appended claims herein, if the thickness of the diaphragm materialis reduced to 0.09 inches, then the gap may be further reduced to2½×0.09=0.225 inches (or 2¼×0.09=0.2025 inches), providing even moreroom for a larger pressure plate.

[0025] Maintaining proper alignment of the larger pressure plate of thepresent invention is important. This may be accomplished in one or moreof several ways. First, an adaptor plate may be employed on the centralshaft of the brake actuator on one side of the diaphragm which works inconjunction with a recessed area on the underside of the pressure plateon the other side of the diaphragm. As the pressure plate moves up anddown, this adaptor plate nestles through the diaphragm into the recessedarea, keeping the pressure plate in central alignment. Alignment mayalso be improved through the use of a bushing/seal retainer in thecenter of the spring housing. Alignment may be further improved byreducing the side load of the main compression spring by grinding downthe exterior surfaces of the end coils of the spring. Traditionally,such springs have a side load of 6 to 8 percent; in the presentinvention, reducing this load to 2 or 3 percent greatly improvesalignment of the main spring in the emergency housing.

[0026] It is to be noted that the improved performance of thediaphragm-based brake actuators of the present invention is accomplishedusing the same circumferential dimensions as existing brake actuatorsusing common membrane diaphragm materials. The diaphragm is not attachedin the center of the actuator, it does not use a moving wall, and itdoes not have any opening or hole in the center thereof.

[0027] Historically, the effective surface area of spring brake pressureplates has been standardized into different types (9, 12, 16 20, 24, 30and 36), each type providing an incrementally larger braking strength.This allows for standard components and parts to be manufactured foreach type. For each type, there is also an incrementally largerassociated profile (size) for the brake actuator. Using the design ofthe present invention, a smaller type (e.g. 24) having a smaller profilemay have the strength of a larger type with a larger profile (e.g. 30).A smaller unit utilizing the features of the present invention may beemployed as a replacement for a larger type, but requiring a smallerspace. In addition, the present invention now makes a new type 43 unitavailable in the space occupied by a type 36.

[0028] It is therefore a primary object of the present invention toprovide a stronger diaphragm-based spring brake actuator unit withoutincreasing the overall size of the unit.

[0029] It is also a primary object of the present invention to provide adiaphragm-based spring brake actuator unit that is able to hold of astronger emergency brake spring without increasing the overall size ofthe unit.

[0030] It is a further primary object of the present invention toprovide a diaphragm-based spring brake actuator unit that is able toprovide more force to the push rod from the service brake assemblywithout increasing the overall size of the unit.

[0031] It is a further important object of the present invention toprovide a stronger diaphragm-based spring brake actuator unit having atlarger pressure plate inside of either the emergency brake housing, theservice brake housing, or both.

[0032] It is a further important object of the present invention toprovide a stronger diaphragm-based spring brake actuator unit havingmore vertical cylindrical walls on the brake housing to accommodate alarger pressure plate inside.

[0033] It is a further important object of the present invention toprovide a stronger diaphragm-based spring brake actuator unit having avery tight gap between the outside circumferential edge of the pressureplate and the inside of the cylindrical wall of the emergency brakehousing to provide more room for a larger pressure plate inside.

[0034] It is a further important object of the present invention toprovide a stronger diaphragm-based spring brake actuator unit having adiaphragm made of thinner material in the emergency brake housing toprovide more room for a larger pressure plate inside.

[0035] It is a further object of the present invention to provide asmaller, stronger diaphragm-based spring brake actuator unit in order toallow for more room for air suspensions and other parts underneath thevehicle to which it is attached.

[0036] It is a further object of the present invention to provide astronger diaphragm-based spring brake actuator unit that isretrofittable onto existing brake assemblies.

[0037] Additional objects of the invention will be apparent from thedetailed descriptions and the claims herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a cross sectional side view of a typical brake actuatorin the normal driving position, the emergency spring being held off bythe pressure of the upper chamber.

[0039]FIG. 2 is a cross sectional side view of a typical brake actuatorin the normal driving position with the service brake being applied bythe vehicle operator.

[0040]FIG. 3 is a cross sectional side view of a typical brake actuatorshowing it in the parked condition, with the emergency spring brakeactivated.

[0041]FIG. 4 is a cross sectional side view of a combined emergency andservice brake actuator of the present invention.

[0042]FIG. 5 is a cross sectional side view of a combined emergency andservice brake actuator of the present invention showing the descendingpositions of the pressure plates of each actuator.

[0043]FIG. 6 is a side view of the present invention comparing itsprofile to an existing competitive brake unit (shown in phantom lines).

[0044]FIG. 7 is an enlarged cross sectional side view of an emergencybrake chamber of the present invention showing the curling of thediaphragm inside the housing as the pressure plate descends.

[0045]FIG. 8 is an enlarged cross sectional side view of a service brakechamber of the present invention.

[0046]FIG. 9 is an enlarged cross sectional side view of a typical priorart actuator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Referring to the drawings wherein like reference charactersdesignate like or corresponding parts throughout the several views, andreferring particularly to the prior art actuator shown in FIGS. 1-3, itis seen that a typical dual diaphragm air brake actuator, generally 20,is comprised of a service brake assembly, generally 30, and an emergencybrake assembly, generally 50. While each of these assemblies may bedeployed independently of the other, when combined the service brakeassembly and emergency brake assembly are in axial alignment with eachother along the path of a push rod 21 which extends out from the centerof one end of the service brake assembly.

[0048] The distal end of push rod 21 extends out from lower servicebrake housing cup 25 and is attached to a clevis 23 which is, in turn,attached to a slack adjuster 24 attached to a rod or cam 26 associatedwith the brakes of a vehicle. Thus, as push rod 21 moves in and out ofthe service brake assembly 30, it exerts force to the brakes of thevehicle. The proximal end of push rod 21 is attached to or closelyassociated with a pressure plate 29 located inside the service brakeassembly 30. A flexible service brake diaphragm 31 is provided insideassembly 30 above plate 29, and is sealed at its edges to define achamber 33 in conjunction with the upper exterior housing 35.

[0049] When pressurized air is introduced into chamber 33, diaphragm 31expands exerting pressure against plate 29 thereby pushing rod 21 out ofassembly 30 as shown in FIG. 2. The application of pressure to chamber33 of the service brake assembly 30 is controlled by the operator of thevehicle through normal operation of the brakes. The amount of pressureapplied to chamber 33 may be varied resulting in a greater or lesserextension of rod 21, and a greater or lesser application of the vehiclebrakes. A retraction spring 37 is provided in lower housing 25 aroundrod 21 to urge plate 29 and rod 21 back inside assembly 30 when airpressure is removed from chamber 33, as shown in FIG. 1.

[0050] The emergency brake assembly 50 includes a lower housing cup 45and an upper housing cup 55. A diaphragm 51 is provided inside assembly50, sealingly attached at its edges-between upper and lower cups 45 and55, to define a chamber 53 in conjunction with the lower housing cup 45.An extension rod 61 having the same diameter and characteristics as pushrod 21 is provided in the center of assembly 50 and inside chamber 53,axially aligned with push rod 21. The distal end of rod 61 extendsthrough a sealed opening at the center of lower housing cup 45 and intothe upper housing cup 35 of the service brake assembly 50. The distalend of rod 61 is attached to a small plate 52 inside service assembly30.

[0051] The proximal end of rod 61 is also attached to a small adaptorpush rod plate 62 located inside chamber 53. Adaptor plate 62 is incontact with diaphragm 51. Above diaphragm 51 is the pressure plate 59of the emergency brake, above which the main compression spring 58 islocated. The lower surface of pressure plate 59 includes a relief area54. By fully pressurizing chamber 53, diaphragm 51 is expanded andpressed against pressure plate 59, compressing main spring 58 into theupper end of housing cup 55, as shown in FIGS. 1 and 2. When pressure isreleased from chamber 53 either by the stopping of the vehicle or from afailure in the pressure system, main spring 58 presses down againstplate 59 pushing diaphragm 51, plate 62 and rod 61 downward. The forceof main spring 58 against plate 59 is transmitted through diaphragm 51to plate 62, rod 61, plate 52, diaphragm 31, plate 29 and rod 21 to thebrakes of the vehicle, as shown in FIG. 3. When such force is exerted,plate 62 nests within the relief area 54 of pressure plate 59.

[0052] Referring to FIGS. 4 and 5, it is seen that the upper pressureplate 59 of the present invention is large, and that the edges of plate59 come very close to the cylindrical side walls of cups 45 and 55.These side walls are vertical or nearly vertical (i.e. they are parallelor nearly parallel to rod 61, and perpendicular or nearly perpendicularto plate 59). The cylindrical wall of cup 55 is only tapered above theuppermost position of plate 59 as shown in FIG. 4. The uprightcylindrical walls of cups 45 and 55 provide a consistently wider spaceinside assembly 50 through which pressure plate 59 may be raised andlowered (see FIG. 5). The gap between the outside circumferential edgeof plate 59 and the inside of the cylindrical walls of cups 45 and 55 isdepicted as “G” in FIG. 5. This gap may be as small as two and one half(2½) times the width (thickness) of diaphragm 51, or smaller. Thisallows sufficient space for diaphragm 51 to fold over itself (i.e. twiceits width) as plate 59 moves up and down, plus a small additional space(½ its width, or less) to avoid unnecessary friction. See FIG. 7. Alesser additional space (resulting in an even larger pressure plate) maybe available with certain low friction diaphragm materials.

[0053] With respect to the service brake housing shown in FIGS. 4 and 5,it is seen that the upper pressure plate 29 of the present invention isalso very large, and that the edges of plate 29 come very close to thecylindrical side walls of cups 25 and 35. These side walls are alsovertical or nearly vertical (i.e. they are parallel or nearly parallelto rod 21, and perpendicular or nearly perpendicular to plate 59). Theupright cylindrical walls of cups 35 and 25 provide a consistently widerspace inside assembly 30 through which pressure plate 29 may be raisedand lowered (see FIG. 5). The gap between the outside circumferentialedge of plate 29 and the inside of the cylindrical walls of cups 25 and35 is depicted as G′ in FIG. 5. This gap may also be as small as two andone half (2½) times the width (thickness) of diaphragm 31, or smaller.This allows sufficient space for diaphragm 31 to fold over itself (i.e.twice its width) as plate 29 moves up and down, plus a small additionalspace (½ its width, or less) to avoid unnecessary friction. A lesseradditional space (resulting in an even larger pressure plate) may beavailable with certain low friction diaphragm materials.

[0054] Diaphragms 31 and 51 may be made of a very thin material. Insteadof an average width of 0.125 inches, diaphragm materials as thin as 0.09inches have been successfully used, and even thinner diaphragm materialsmay also be used. Using a standard diaphragm of 0.125 inches, gaps G andG′ (at 2½ times this thickness) could be as small as 0.3125 inches.Reducing the diaphragm thickness to 0.09 inches results in a gap G or G′as small as 0.225 inches. Using a low friction material may allow a gapG or G′ of 2¼ times its thickness which, for the 0.09 diaphragm wouldresult in a very small gap G or G′ of 0.2025 inches. A thinner diaphragmmaterial will reduce gap G or G′ even further. Each of thesemodifications, used together or separately, allows for a larger pressureplate to be installed inside the housing.

[0055] The smallest known gap G or G′ in an existing brake actuator is0.57 inches using a diaphragm having a thickness of 0.125 inches (seeFIG. 9). This gives a ratio of diaphragm thickness to gap size of1:4.56. The present invention provides a smaller ratio which can be aslow as 1:2.5 or lower. Embodiments having a ratio of diaphragm thicknessto gap size ranging from 1:4.56 to 1:2.5 or smaller will allow everincreasing space for larger and larger pressure plates 29 and 59. Thisprovides for a range of pressure plate sizes and corresponding strengthsfor the main compression spring 58 within the emergency housing, and forthe available braking strength in the service housing.

[0056] The area (A) of a circle such as the pressure plates 29 and 59 ofthe present invention is determined according to the well known formulaA=πR² where (R) is the radius of the circle defined by the pressureplate, and π=approximately 3.14159. This formula may also be stated asA=¼πD² where (D) is the diameter of the circle defined by the pressureplate. See FIG. 5 where D and R are used for plate 59, and D′ and R′ areused for plate 29. The inside sectional area of the cylindrical housingcups (55 and 45 in the emergency brake housing, and 35 and 25 in theservice brake housing) may also be defined by the same formulas, where Dis the diameter of the available inside circumferential wall of cups 55and 45 in the emergency brake housing, and D′ for the cups 35 and 25 inthe service brake housing.

[0057] Using the above formulas, the possible areas (A) for pressureplate 59 relative to gap G defined by the present invention range fromas large as about π(R-2.5 x)² to as small as about π(R-4.56 x)² where“R” is the radius of the inside circumferential wall of cups 55 and 45through which plate 59 travels, and “x” is the thickness of thediaphragm 51. Stated with the other formula, the range is from about¼π(D-5 x)² to about ¼π(D-9.12 x)². For illustrative purposes and by wayof example only, and without limiting the scope of the appended claimsherein, if the available inside diameter (D) of the housing cups 45 and55 is eight inches (8″), and a diaphragm 51 having a thickness “x” ofone eighth inch (0.125″) is employed, then the possible area (A) sizesfor plate 59 defined by the present invention range from about 42.718 toabout 36.961 square inches [¼π(7.375)² to ¼π(6.86)²]. Employing adiaphragm 51 having a thickness “x” of 0.09 inches in this exampleresults in a larger area (A) range for plate 59 of between about 44.77and about 40.48 square inches. Straightening the outside walls of cups45 and 55 to create an available diameter of more than eight inches willincrease the available area (A) for plate 59 even more.

[0058] These same principles also apply to the service brake assembly 30defined by cups 25 and 35, and using pressure plate 29. Using the aboveformulas, the possible areas (A) for the pressure plate 29 relative togap G′ defined by the present invention range from as large as aboutπ(R′-2.5 x)² to as small as about π(R′-4.566 x)² where R′ is the radiusof the inside circumferential wall of cups 35 and 25 through which plate29 travels, and “x” is the thickness of the diaphragm 31. Stated withthe other formula, the range is from about ¼π(D′-5 x)² to about{fraction (1/4)}π(D′-9.12 x)². Employing a thinner diaphragm 31 and/orstraightening the outside walls of cups 35 and 25 to create a largeravailable inside diameter will increase the available area (A) for plate29 even more.

[0059] The circumference of plate 59 (or 29) is defined by the formula2πR (2πR′ for plate 29) or πD (πD′ for plate 29). Using this formula,the range of circumference for plate 59 ranges from as large as about2π(R-2.5 x) to as small as about 2π(R-4.56 x) where R is the radius ofthe inside circumferential wall of cups 45 and 55 through which plate 59travels, and “x” is the thickness of the diaphragm 51. The same formulasapply to the service brake using R′ for the inside circumferential wallof cups 25 and 35 through which plate 29 travels, and “x′” for thethickness of diaphragm 31: about 2π(R′-2.5 x′) to as small as about2π(R′-4.563 x′).

[0060] Stated with the other formula, the range in circumference for theplate is from about π(D-5 x) to about π(D′-9.12 x). Employing a thinnerdiaphragm 31 (or 51) and/or straightening the outside walls of cups 35and 25 (or 45 and 55) to create a larger available inside diameter willincrease the available circumference for plate 29 (or 59) even more.

[0061] The improvements of the present invention may be applied to asingle-diaphragm stand alone service brake actuator, to asingle-diaphragm stand alone emergency brake actuator, or to a combinedservice and emergency brake actuator.

[0062] It is to be understood that variations and modifications of thepresent invention may be made without departing from the scope thereof.It is also to be understood that the present invention is not to belimited by the specific embodiments disclosed herein, but only inaccordance with the appended claims when read in light of the foregoingspecification.

We claim:
 1. An improved brake actuating mechanism comprising a housingwith first and second end walls, an elastomeric diaphragm suspendedwithin said housing and being sealingly attached to the edges thereof toform at least one chamber therein, a large circular pressure platehorizontally deployed in said housing and having a flat portion adjacentto said diaphragm, said pressure plate being associated with a brakeactuating rod disposed in said housing and extending through a centrallydisposed opening in the first end wall for reciprocating movementrelative to the housing, wherein the side wall of said housing has agenerally cylindrical shape relative to said end walls, and said sidewall has a nearly vertical orientation relative to said pressure plate.2. The mechanism of claim 1 wherein the area of said pressure plate ismaximized by reducing the gap between the outside circumferential edgeof said circular pressure plate and the inside cylindrical side wallthrough which said plate travels to a size that is between about 2¼ andabout 4½ times the thickness of said diaphragm.
 3. The mechanism ofclaim 1 wherein the area of said pressure plate is maximized by reducingthe gap between the outside circumferential edge of said circularpressure plate and the inside cylindrical side wall through which saidplate travels to a size that is between about 2½ and about 4 times thethickness of said diaphragm.
 4. The mechanism of claim 1 wherein the gapbetween the outside circumferential edge of said circular pressure plateand the inside of said cylindrical side wall through which said platetravels is greater than about twice the thickness of said diaphragm andless than about 0.57 inches.
 5. The mechanism of claim 1 wherein the gapbetween the outside circumferential edge of said circular pressure plateand the inside of said cylindrical side wall through which said platetravels is greater than about twice the thickness of said diaphragm andless than about 0.5 inches.
 6. The mechanism of claim 1 wherein thecircumference of said plate is greater than about 2π(R-4.56 x) wherein xis the thickness of said diaphragm, R is the radius of the inside ofsaid cylindrical side wall through which said plate travels.
 7. Themechanism of claim 1 wherein the circumference of said plate is greaterthan about 2π(R-4.5 x) wherein x is the thickness of said diaphragm, Ris the radius of the inside of said cylindrical side wall through whichsaid plate travels.
 8. The mechanism of claim 1 wherein thecircumference of said plate is between about 2π(R-4.56 x) and about2π(R-2.25 x) relative to said diaphragm and said housing wherein x isthe thickness of said diaphragm, R is the minimum radius of the insideof said cylindrical side wall through which said plate travels.
 9. Themechanism of claim 1 wherein the circumference of said plate is betweenabout 2π(R-4.5 x) and about 2π(R-2.5 x) relative to said diaphragm andsaid housing wherein x is the thickness of said diaphragm, R is theminimum radius of the inside of said cylindrical side wall through whichsaid plate travels.
 10. The mechanism of claim 2 wherein the area ofsaid pressure plate is further maximized by reducing the thickness ofsaid diaphragm.
 11. The mechanism of claim 10 wherein said diaphragm hasa thickness of between 0.09 inches and 0.125 inches.
 12. The mechanismof claim 3 wherein the area of said pressure plate is further maximizedby reducing the thickness of said diaphragm.
 13. The mechanism of claim12 wherein said diaphragm has a thickness of between 0.09 inches and0.125 inches.
 14. The mechanism of claim 8 wherein the area of saidpressure plate is further maximized by reducing the thickness of saiddiaphragm.
 15. The mechanism of claim 14 wherein said diaphragm has athickness of between 0.09 inches and 0.125 inches.
 16. The mechanism ofclaim 9 wherein the area of said pressure plate is further maximized byreducing the thickness of said diaphragm.
 17. The mechanism of claim 16wherein said diaphragm has a thickness of between 0.09 inches and 0.125inches.
 18. An air-operated brake assembly for a vehicle comprising aservice brake housing, a spring brake housing arranged in tandem withand attached to said service brake housing, a brake actuating push rodhaving one end extending outwardly from said service brake housing andanother end disposed internally of said service brake housing forreciprocating motion relative thereto, an actuator rod disposed in saidspring brake housing in alignment with said brake actuating push rod, anelastomeric diaphragm suspended within said spring brake housing andbeing sealingly attached to the edges thereof to form at least onechamber therein, a main compression spring disposed in said spring brakehousing having one end engaging a generally horizontal end wall of saidspring brake housing, a large circular pressure plate horizontallydeployed in said spring brake housing between said main compressionspring and said diaphragm and having a flat portion adjacent to saiddiaphragm, said pressure plate being associated with said actuator rod,wherein the side wall of said spring brake housing has a generallycylindrical shape, and said side wall has a nearly vertical orientationrelative to said end wall and pressure plate.
 19. The brake assembly ofclaim 18 wherein a compression spring is provided in said service brakehousing acting on said push rod urging said push rod toward a retractedposition, a second elastomeric diaphragm is suspended within saidservice brake housing and being sealingly attached to the edges thereofto form at least one chamber therein, a second large flat circularpressure plate is horizontally deployed in said service brake housingadjacent to said diaphragm, said second pressure plate being attached tosaid push rod, wherein the side wall of said service brake housing has agenerally cylindrical shape, and said service brake side wall has anearly vertical orientation relative to said second pressure plate. 20.The mechanism of claim 19 wherein the area of each of said pressureplates is maximized by reducing the gap between the outsidecircumferential edge of each such plate and the inside cylindrical sidewall through which each such plate travels to a size that is betweenabout 2¼ and about 4½ times the thickness of the diaphragm adjacent tosuch plate.
 21. The mechanism of claim 19 wherein the area of each ofsaid pressure plates is maximized by reducing the gap between theoutside circumferential edge of each such plate and the insidecylindrical side wall through which each such plate travels to a sizethat is between about 2½ and about 4 times the thickness of thediaphragm adjacent to such plate.
 22. The mechanism of claim 19 whereinthe gap between the outside circumferential edge of each such plate andthe inside of said cylindrical side wall through which each such platetravels is greater than about twice the thickness of the diaphragmadjacent to such plate and less than about 0.57 inches.
 23. Themechanism of claim 19 wherein the gap between the outsidecircumferential edge of each such plate and the inside of saidcylindrical side wall through which each such plate travels is greaterthan about twice the thickness of the diaphragm adjacent to such plateand less than about 0.5 inches.
 24. The mechanism of claim 19 whereinthe circumference of each plate is greater than about 2π(R-4.56 x)wherein x is the thickness of the diaphragm adjacent to such plate, R isthe radius of the inside of said cylindrical side wall through whicheach such plate travels.
 25. The mechanism of claim 19 wherein thecircumference of each plate is greater than about 2π(R-4.5 x) wherein xis the thickness of the diaphragm adjacent to such plate, R is theradius of the inside of said cylindrical side wall through which eachsuch plate travels.
 26. The mechanism of claim 19 wherein thecircumference of each plate is between about 2π(R-4.56 x) and about2π(R-2.25 x) relative to the diaphragm adjacent to such plate and thehousing wall through which such plate travels wherein x is the thicknessof the diaphragm adjacent to such plate, R is the minimum radius of theinside of said cylindrical side wall through which each such platetravels.
 27. The mechanism of claim 19 wherein the circumference of eachplate is between about 2π(R-4.5 x) and about 2π(R-2.5 x) relative to thediaphragm adjacent to such plate and the housing wall through which suchplate travels wherein x is the thickness of the diaphragm adjacent tosuch plate, R is the minimum radius of the inside of said cylindricalside wall through which each such plate travels.
 28. The mechanism ofclaim 20 wherein the area of each of said pressure plates is furthermaximized by reducing the thickness of the diaphragm adjacent to suchplate.
 29. The mechanism of claim 28 wherein the diaphragm adjacent toeach plate has a thickness of between 0.09 inches and 0.125 inches. 30.The mechanism of claim 21 wherein the area of each of said pressureplates is further maximized by reducing the thickness of the diaphragmadjacent to such plate.
 31. The mechanism of claim 30 wherein thediaphragm adjacent to each plate has a thickness of between 0.09 inchesand 0.125 inches.
 32. The mechanism of claim 26 wherein the area of eachof said pressure plates is further maximized by reducing the thicknessof the diaphragm adjacent to such plate.
 33. The mechanism of claim 32wherein the diaphragm adjacent to each plate has a thickness of between0.09 inches and 0.125 inches.
 34. The mechanism of claim 27 wherein thearea of each of said pressure plates is further maximized by reducingthe thickness of the diaphragm adjacent to such plate.
 35. The mechanismof claim 34 wherein the diaphragm adjacent to each plate has a thicknessof between 0.09 inches and 0.125 inches.
 36. A spring brake assemblycomprising a housing having end walls, a brake actuating push rod havingone end extending outwardly from said housing and another end disposedinternally of said housing for reciprocating motion relative thereto, anelastomeric diaphragm suspended within said spring brake housing andbeing sealingly attached to the edges thereof to form at least onechamber therein, a main compression spring disposed in said housinghaving one end engaging a generally horizontal end wall of said housing,a large circular pressure plate horizontally deployed in said housingbetween said main compression spring and said diaphragm and having aflat portion adjacent to said diaphragm, said pressure plate beingassociated with said push rod, wherein the side wall of said housing hasa generally cylindrical shape, and said side wall has a nearly verticalorientation relative to said end walls and said pressure plate.
 37. Themechanism of claim 36 wherein the area of said pressure plate ismaximized by reducing the gap between the outside circumferential edgeof said circular pressure plate and the inside cylindrical side wallthrough which said plate travels to a size that is between about 2¼ andabout 4½ times the thickness of said diaphragm.
 38. The mechanism ofclaim 36 wherein the area of said pressure plate is maximized byreducing the gap between the outside circumferential edge of saidcircular pressure plate and the inside cylindrical side wall throughwhich said plate travels to a size that is between about 2½ and about 4times the thickness of said diaphragm.
 39. The mechanism of claim 36wherein the gap between the outside circumferential edge of saidcircular pressure plate and the inside of said cylindrical side wallthrough which said plate travels is greater than about twice thethickness of said diaphragm and less than about 0.57 inches.
 40. Themechanism of claim 36 wherein the gap between the outsidecircumferential edge of said circular pressure plate and the inside ofsaid cylindrical side wall through which said plate travels is greaterthan about twice the thickness of said diaphragm and less than about 0.5inches.
 41. The mechanism of claim 36 wherein the circumference of saidplate is greater than about 2π(R-4.56 x) wherein x is the thickness ofsaid diaphragm, R is the radius of the inside of said cylindrical sidewall through which said plate travels.
 42. The mechanism of claim 36wherein the circumference of said plate is greater than about 2π(R-4.5x) wherein x is the thickness of said diaphragm, R is the radius of theinside of said cylindrical side wall through which said plate travels.43. The mechanism of claim 36 wherein the circumference of said plate isbetween about 2π(R-4.56 x) and about 2π(R-2.25 x) relative to saiddiaphragm and said housing wherein x is the thickness of said diaphragm,R is the minimum radius of the inside of said cylindrical side wallthrough which said plate travels.
 44. The mechanism of claim 36 whereinthe circumference of said plate is between about 2π(R-4.5 x) and about2π(R-2.5 x) relative to said diaphragm and said housing wherein x is thethickness of said diaphragm, R is the minimum radius of the inside ofsaid cylindrical side wall through which said plate travels.
 45. Themechanism of claim 37 wherein the area of said pressure plate is furthermaximized by reducing the thickness of said diaphragm.
 46. The mechanismof claim 45 wherein said diaphragm has a thickness of between 0.09inches and 0.125 inches.
 47. The mechanism of claim 38 wherein the areaof said pressure plate is further maximized by reducing the thickness ofsaid diaphragm.
 48. The mechanism of claim 47 wherein said diaphragm hasa thickness of between 0.09 inches and 0.125 inches.
 49. The mechanismof claim 43 wherein the area of said pressure plate is further maximizedby reducing the thickness of said diaphragm.
 50. The mechanism of claim49 wherein said diaphragm has a thickness of between 0.09 inches and0.125 inches.
 51. The mechanism of claim 44 wherein the area of saidpressure plate is further maximized by reducing the thickness of saiddiaphragm.
 52. The mechanism of claim 51 wherein said diaphragm has athickness of between 0.09 inches and 0.125 inches.
 53. A service brakeassembly comprising a housing having end walls, a brake actuating pushrod having one end extending outwardly from said housing and another enddisposed internally of said housing for reciprocating motion relativethereto, a compression spring provided in said housing acting on saidpush rod urging said push rod toward a retracted position, anelastomeric diaphragm suspended within said housing and being sealinglyattached to the edges thereof to form at least one chamber therein, alarge flat circular pressure plate horizontally deployed in said housingadjacent to said diaphragm, said pressure plate being attached to saidpush rod, wherein the side wall of said service brake housing has agenerally cylindrical shape, and said side wall has a nearly verticalorientation relative to said pressure plate.
 54. The mechanism of claim53 wherein the area of said pressure plate is maximized by reducing thegap between the outside circumferential edge of said circular pressureplate and the inside cylindrical side wall through which said platetravels to a size that is between about 2¼ and about 4½ times thethickness of said diaphragm.
 55. The mechanism of claim 53 wherein thearea of said pressure plate is maximized by reducing the gap between theoutside circumferential edge of said circular pressure plate and theinside cylindrical side wall through which said plate travels to a sizethat is between about 2¼ and about 4 times the thickness of saiddiaphragm.
 56. The mechanism of claim 53 wherein the gap between theoutside circumferential edge of said circular pressure plate and theinside of said cylindrical side wall through which said plate travels isgreater than about twice the thickness of said diaphragm and less thanabout 0.57 inches.
 57. The mechanism of claim 53 wherein the gap betweenthe outside circumferential edge of said circular pressure plate and theinside of said cylindrical side wall through which said plate travels isgreater than about twice the thickness of said diaphragm and less thanabout 0.5 inches.
 58. The mechanism of claim 53 wherein thecircumference of said plate is greater than about 2π(R-4.56 x) wherein xis the thickness of said diaphragm, R is the radius of the inside ofsaid cylindrical side wall through which said plate travels.
 59. Themechanism of claim 53 wherein the circumference of said plate is greaterthan about 2π(R-4.5 x) wherein x is the thickness of said diaphragm, Ris the radius of the inside of said cylindrical side wall through whichsaid plate travels.
 60. The mechanism of claim 53 wherein thecircumference of said plate is between about 2π(R-4.56 x) and about2π(R-2.25 x) relative to said diaphragm and said housing wherein x isthe thickness of said diaphragm, R is the minimum radius of the insideof said cylindrical side wall through which said plate travels.
 61. Themechanism of claim 53 wherein the circumference of said plate is betweenabout 2π(R-4.5 x) and about 2π(R-2.5 x) relative to said diaphragm andsaid housing wherein x is the thickness of said diaphragm, R is theminimum radius of the inside of said cylindrical side wall through whichsaid plate travels.
 62. The mechanism of claim 54 wherein the area ofsaid pressure plate is further maximized by reducing the thickness ofsaid diaphragm.
 63. The mechanism of claim 62 wherein said diaphragm hasa thickness of between 0.09 inches and 0.125 inches.
 64. The mechanismof claim 55 wherein the area of said pressure plate is further maximizedby reducing the thickness of said diaphragm.
 65. The mechanism of claim64 wherein said diaphragm has a thickness of between 0.09 inches and0.125 inches.
 66. The mechanism of claim 60 wherein the area of saidpressure plate is further maximized by reducing the thickness of saiddiaphragm.
 67. The mechanism of claim 66 wherein said diaphragm has athickness of between 0.09 inches and 0.125 inches.
 68. The mechanism ofclaim 61 wherein the area of said pressure plate is further maximized byreducing the thickness of said diaphragm.
 69. The mechanism of claim 68wherein said diaphragm has a thickness of between 0.09 inches and 0.125inches.
 70. In a fluid pressure-operated diaphragm spring brake having ahousing, an elastomeric diaphragm suspended within said housing andbeing sealingly attached to the edges thereof to form at least onechamber therein, a large circular pressure plate horizontally deployedin said housing and having a flat portion adjacent to said diaphragm,said pressure plate being associated with a brake actuating rod disposedin said housing and extending through a centrally disposed opening inthe first end wall for reciprocating movement relative to the housing,the improvement wherein the side wall of said housing has a generallycylindrical shape relative to said end walls, and said side wall has anearly vertical orientation relative to said pressure plate.
 71. Themechanism of claim 70 wherein the area of said pressure plate ismaximized by reducing the gap between the outside circumferential edgeof said circular pressure plate and the inside cylindrical side wallthrough which said plate travels to a size that is between about 2¼ andabout 4½ times the thickness of said diaphragm.
 72. The mechanism ofclaim 70 wherein the area of said pressure plate is maximized byreducing the gap between the outside it circumferential edge of saidcircular pressure plate and the inside cylindrical side wall throughwhich said plate travels to a size that is between about 2½ and about 4times the thickness of said diaphragm.
 73. The mechanism of claim 70wherein the gap between the outside circumferential edge of saidcircular pressure plate and the inside of said cylindrical side wallthrough which said plate travels is greater than about twice thethickness of said diaphragm and less than about 0.57 inches.
 74. Themechanism of claim 70 wherein the gap between the outsidecircumferential edge of said circular pressure plate and the inside ofsaid cylindrical side wall through which said plate travels is greaterthan about twice the thickness of said diaphragm and less than about 0.5inches.
 75. The mechanism of claim 70 wherein the circumference of saidplate is greater than about 2π(R-4.56 x) wherein x is the thickness ofsaid diaphragm, R is the radius of the inside of said cylindrical sidewall through which said plate travels.
 76. The mechanism of claim 70wherein the circumference of said plate is greater than about 2π(R-4.5x) wherein x is the thickness of said diaphragm, R is the radius of theinside of said cylindrical side wall through which said plate travels.77. The mechanism of claim 70 wherein the circumference of said plate isbetween about 2π(R-4.56 x) and about 2π(R-2.25 x) relative to saiddiaphragm and said housing wherein x is the thickness of said diaphragm,R is the minimum radius of the inside of said cylindrical side wallthrough which said plate travels.
 78. The mechanism of claim 70 whereinthe circumference of said plate is between about 2π(R-4.5 x) and about2π(R-2.5 x) relative to said diaphragm and said housing wherein x is thethickness of said diaphragm, R is the minimum radius of the inside ofsaid cylindrical side wall through which said plate travels.
 79. Themechanism of claim 71 wherein the area of said pressure plate is furthermaximized by reducing the thickness of said diaphragm.
 80. The mechanismof claim 79 wherein said diaphragm has a thickness of between 0.09inches and 0.125 inches.
 81. The mechanism of claim 72 wherein the areaof said pressure plate is further maximized by reducing the thickness ofsaid diaphragm.
 82. The mechanism of claim 81 wherein said diaphragm hasa thickness of between 0.09 inches and 0.125 inches.
 83. The mechanismof claim 77 wherein the area of said pressure plate is further maximizedby reducing the thickness of said diaphragm.
 84. The mechanism of claim83 wherein said diaphragm has a thickness of between 0.09 inches and0.125 inches.
 85. The mechanism of claim 78 wherein the area of saidpressure plate is further maximized by reducing the thickness of saiddiaphragm.
 86. The mechanism of claim 85 wherein said diaphragm has athickness of between 0.09 inches and 0.125 inches.